Two dimensional XAs (X = Si, Ge, Sn) monolayers as promising photocatalysts for water splitting hydrogen production with high carrier mobility

Abstract Two dimensional (2D) materials are emerging as promising candidates for photocatalysts owing to their fascinating properties and ultra-high specific areas. Herein, using first principle calculations, we systematically investigated a new kind of 2D XAs (X = Si, Ge, Sn). After verifying their stabilities, we found that SiAs and SnAs monolayers possess direct band gaps of 2.35 and 1.69 eV, while GeAs has an indirect band gap of 2.08 eV by HSE hybrid functional with the inclusion of spin-orbit coupling (SOC) effect. Meanwhile, their exceptionally high and directionally anisotropic carrier mobilities (up to 8.98 × 103 cm2 V−1 s−1 for SiAs) can be advantageous for the fast migration and separation of the photogenerated electron-hole pairs. Most importantly, their band gaps and band edge positions at neutral environment meet the requirement of water splitting. Moreover, the study of XAs heterobilayers (correspondingly stacking with GaS, GaSe and InSe monolayers) shows that they have type-II band alignment, enhanced optical absorption and proper CBM positions with respect to the reduction potential of water, indicating that they may have stronger driving force for the hydrogen evolution reaction. Finally, we explored the adsorption and decomposition of water as well as the subsequent generation of hydrogen on the surfaces of 2D SiAs and SiAs/GaS, which unravels the micro-mechanism of the photocatalytic hydrogen production process. Our finding shows that XAs monolayers can provide appealing alternatives for diverse nanodevices and be potential candidates for metal-free photocatalysts.